CN117394281A - Protection method and system for open-phase and three-phase voltage unbalance of frequency converter - Google Patents
Protection method and system for open-phase and three-phase voltage unbalance of frequency converter Download PDFInfo
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- CN117394281A CN117394281A CN202311232049.5A CN202311232049A CN117394281A CN 117394281 A CN117394281 A CN 117394281A CN 202311232049 A CN202311232049 A CN 202311232049A CN 117394281 A CN117394281 A CN 117394281A
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
- H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
- H02H7/1216—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for AC-AC converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/24—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to undervoltage or no-voltage
- H02H3/253—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to undervoltage or no-voltage for multiphase applications, e.g. phase interruption
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/14—Arrangements for reducing ripples from dc input or output
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Abstract
The invention discloses a protection method and a system for open-phase and three-phase voltage unbalance of a frequency converter, comprising the following steps: acquiring a voltage vector of an alternating component of the direct-current bus voltage; obtaining the basic value angular frequency of the alternating current component of the direct current bus voltage; acquiring the actual angular frequency and amplitude of the alternating current component of the direct current bus voltage; judging whether phase loss, unbalance degree of three-phase voltage and whether current limiting treatment is needed or not according to the relation between the actual angular frequency of the alternating current component of the direct current bus voltage and the angular frequency of the power grid; if necessary, current limiting protection is performed according to ripple current of the DC bus capacitor when three phases are unbalanced. The invention is used for solving the technical problems of no input open-phase protection, no three-phase voltage unbalance protection, additional cost increase through hardware protection and reliability reduction of the existing frequency converter, thereby achieving the purpose of improving the running reliability of the frequency converter.
Description
Technical Field
The invention relates to the technical field of frequency converter protection, in particular to a protection method and a protection system for phase loss and three-phase voltage unbalance of a frequency converter.
Background
The topology of the frequency converter for three-phase power input is shown in fig. 1. In fig. 1, L2, L3 are power input three-phase live wires; REC is a rectifier that rectifies the input three-phase alternating current into direct current; the Reactor is a Reactor, and functions to suppress abrupt change of input current and improve input power factor; c is a direct current bus capacitor, generally an electrolytic capacitor or a polypropylene film capacitor, and is used for filtering the rectified voltage containing ripple waves to change the rectified voltage into stable direct current voltage; the IPM is an inversion module or a frequency conversion module and is used for inverting the direct-current voltage into the alternating-current voltage required by the motor; m is motor load, which can be AC asynchronous motor, permanent magnet synchronous motor, or the motor and load integrated fan, compressor, pump, etc.
Under the condition of three-phase voltage input open-phase, the existing frequency converter is easy to exceed the design range when in heavy load, so that a fuse tube is burnt out, or a rectifier is damaged, or a direct current bus capacitor is overheated and damaged. Or in the case of unbalanced three-phase input voltage, the current of the lowest phase decreases and the current of the highest phase increases, and the current of the highest phase exceeds the design range during heavy load, resulting in the same result as phase failure. Therefore, in order to prevent the hidden trouble caused by phase loss or three-phase imbalance, an additional hardware protection circuit is often required to be added, but the circuit design is complicated, the cost is increased, and the reliability is lowered.
Aiming at the defects of the hardware solution, the MCU is proposed to sample the voltage of a direct current bus, carry out high-pass filtering to obtain an alternating current component, then carry out zero crossing comparison to obtain the frequency of the alternating current component, further calculate the amplitude value in one period, judge whether the phase is out of phase or not and the three-phase voltage is unbalanced according to the frequency and the amplitude value, but the possibility of misjudgment exists in the method, and the reliability is poor. In addition, it is difficult to identify the situation in which protection should be triggered, for the following reasons:
in normal operation, the voltage across the capacitor, i.e., the dc bus voltage, contains an ac component, the frequency of which is 6 times the frequency of the input voltage, and if the input voltage frequency is 50Hz, the voltage frequency of the dc bus ac component is 300Hz, and the waveform is shown in fig. 2.
When a certain phase is broken, the power frequency of the ac component of the dc bus voltage is the frequency of the input voltage, and the waveform is shown in fig. 3.
When a three-phase voltage imbalance occurs, the fundamental frequency of the power supply of the ac component of the dc bus voltage remains the frequency of the input voltage, but also contains a 6 th harmonic component, the magnitude of which is related to the degree of imbalance. Typical waveforms for different imbalances are shown in fig. 4 and 5. Fig. 4 shows a waveform with small unbalance, and fig. 5 shows a waveform with large unbalance.
From the three conditions, it can be found that the protection is easiest to judge when the phase is out of phase and the phase is not out of phase, but is harder to judge when the three-phase input voltage is unbalanced, and it is difficult to identify under what condition the protection should be triggered.
The waveform only shows the time characteristics of the voltage of the direct current bus under different conditions, and the actual condition is influenced by various factors such as input voltage frequency fluctuation, load size, frequency converter control mode and the like, and the waveform is not an ideal curve, so that the difficulty of identification is increased.
In summary, the prior art lacks an effective technical means for input open-phase protection and three-phase voltage unbalance protection of the frequency converter without adding an additional hardware protection circuit.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a protection method and a system for phase failure and three-phase voltage unbalance of a frequency converter, which are used for solving the technical problems of no input phase failure protection and no three-phase voltage unbalance protection of the existing frequency converter, and additionally increasing cost and reducing reliability through hardware protection, thereby achieving the purpose of improving the operation reliability of the frequency converter.
In order to solve the problems, the technical scheme adopted by the invention is as follows:
a protection method for phase loss and three-phase voltage unbalance of a frequency converter comprises the following steps:
acquiring a voltage vector of an alternating component of the direct-current bus voltage;
obtaining the basic value angular frequency of the alternating current component of the direct current bus voltage;
acquiring the actual angular frequency and amplitude of the alternating current component of the direct current bus voltage;
judging whether phase loss, unbalance degree of three-phase voltage and whether current limiting treatment is needed or not according to the relation between the actual angular frequency of the alternating current component of the direct current bus voltage and the angular frequency of the power grid;
if necessary, current limiting protection is performed according to ripple current of the DC bus capacitor when three phases are unbalanced.
In a preferred embodiment of the present invention, the method for acquiring a voltage vector of an ac component of a dc bus voltage includes:
MCU detects direct current busbar voltage V dc Filtering alternating current components by a low pass filter LPF to obtain stable direct current voltageAs shown in equation 1:
wherein omega is LPF The cut-off frequency of the low-pass filter is the power supply voltage frequency omega g 0.1-0.2 times of the number, s is a Lawster operator;
according to the DC bus voltage V dc And the stable DC voltageObtaining a voltage vector of an alternating current componentAs shown in equation 2:
in a preferred embodiment of the present invention, the method for obtaining the fundamental angular frequency of the ac component of the dc bus voltage includes:
obtaining voltage vector of DC bus voltage AC componentAnd obtaining a basic value angular frequency according to the MCU sampling time, as shown in a formula 3:
wherein N is the count value of zero crossing point, T s Sampling time omega for MCU 1 Is the base angular frequency.
In a preferred embodiment of the present invention, the method for acquiring the actual angular frequency and amplitude of the ac component of the dc bus voltage includes:
voltage vector for AC component of DC bus voltageDecomposed into a pair of orthogonal vectors in a stationary coordinate systemAnd->
The orthogonal vector is processedAnd->Conversion into orthogonal DC signals by synchronous rotation of the coordinate system>Andand controlling the phase angle frequency Deltaω with the fundamental wave angle frequency omega by proportional integral 1 I.e. the actual angular frequency ω;
wherein the method comprises the steps ofConverting the actual angular frequency omega into a phase angle theta through an integrator, wherein the phase angle theta is an angle required by converting the static coordinate system into the synchronous rotation coordinate system; the q-axis component setting value in the synchronous rotation coordinate system is 0 whenWhen the phase-locked loop is equal to 0, the phase locking of the phase-locked loop is stable; d-axis component in said synchronous rotation coordinate system +.>Is the amplitude of the alternating component of the direct current bus voltage.
In a preferred embodiment of the present invention, when judging whether or not a phase is lost, unbalance of three-phase voltages, and whether or not current limiting processing is required, the method includes:
when the actual angular frequency omega and the grid angular frequency omega g The method meets the following conditions: omega is greater than or equal to k 1 ω g When the three-phase input voltage of the power grid is normal, or the voltage unbalance is in an acceptable range, the frequency converter can normally operate;
wherein k is 1 Scaling factors set for the program.
In a preferred embodiment of the present invention, when judging whether or not a phase is lost, unbalance of three-phase voltages, and whether or not current limiting processing is required, the method includes:
when the actual angular frequency omega and the grid angular frequency omega g The method meets the following conditions: omega < k 1 ω g When the three-phase unbalance is serious, the frequency converter is possibly caused to be faulty, and at the moment, ripple current of the direct-current bus capacitor is required to be obtained according to the alternating-current component of the direct-current bus voltage to carry out current limiting treatment;
wherein k is 1 Scaling factors set for the program.
In a preferred embodiment of the present invention, when judging whether or not a phase is lost, unbalance of three-phase voltages, and whether or not current limiting processing is required, the method includes:
when the actual angular frequency omega and the grid angular frequency omega g The method meets the following conditions: omega < k 2 ω g When the three-phase unbalance is serious and even the phase failure occurs, the machine is required to be stopped for alarming;
wherein k is 2 Scaling factors set for the program.
As a preferred embodiment of the present invention, when current limiting protection is performed in a three-phase imbalance based on ripple current of a dc bus capacitor, the present invention includes:
the actual ripple current of the dc bus capacitor is obtained as shown in equations 4 and 5:
wherein ω is angular frequency, t is time,for phase angle, < >>Is the amplitude of the alternating component of the direct current bus voltage,a voltage vector which is the alternating component of the direct current bus voltage, C is the capacitance of the direct current bus capacitor, i C The actual ripple current of the DC bus capacitor;
and obtaining the peak value of the actual ripple current through the actual ripple current, and carrying out current limiting processing based on the peak value of the actual ripple current.
As a preferred embodiment of the present invention, when the peak value of the actual ripple current is obtained, as shown in formula 6:
wherein I is CM Peak value of actual ripple current;
when current limiting processing is performed based on the peak value of the actual ripple current, the method comprises the following steps:
when I CM ≤I CM0 -ΔI set1 When the current limiting process is not performed;
when I CM ≤I CMO -ΔI set2 Limiting the load rotation speed to increase so as to limit the ripple current to increase;
when I CM ≥I CM0 When the load rotating speed is reduced, the ripple current is reduced;
when I CM0 -ΔI set2 ＜I CM ＜I CM0 When the current rotating speed is maintained;
wherein I is CM0 Is the rated ripple current of the DC bus capacitor, delta I set1 、ΔI set2 Is the set current threshold.
A protection system for a frequency converter open-phase and three-phase voltage imbalance, comprising:
a voltage vector acquisition unit: the voltage vector is used for acquiring the alternating-current component of the direct-current bus voltage;
basic value angular frequency acquisition unit: the base value angular frequency is used for acquiring the alternating current component of the direct current bus voltage;
actual angular frequency and amplitude acquisition unit: the method comprises the steps of acquiring actual angular frequency and amplitude of alternating current components of direct current bus voltage;
phase failure and unbalance degree judging unit: the method is used for judging whether phase loss, unbalance degree of three-phase voltage and whether current limiting treatment is needed or not according to the relation between the actual angular frequency of the alternating current component of the direct current bus voltage and the angular frequency of the power grid;
current limiting protection unit: the current limiting device is used for carrying out current limiting protection when three-phase unbalance is carried out according to ripple current of the direct current bus capacitor when current limiting treatment is needed.
Compared with the prior art, the invention has the beneficial effects that:
(1) The invention extracts the frequency, the phase and the amplitude of the alternating current component of the direct current bus voltage based on the phase-locked loop technology of the synchronous rotation coordinate system, has one of the advantages of stronger anti-interference capability, is not influenced by the change of the power supply frequency, the change of the amplitude or the simultaneous change of the power supply frequency and the amplitude, and is not influenced by the load size; secondly, the accuracy is high, and the fundamental wave frequency and the 6 th harmonic frequency of the alternating current component can be accurately extracted;
(2) On the premise of not increasing hardware cost, the invention realizes the open-phase and three-phase unbalanced protection of the frequency converter by designing a detection algorithm based on the DC bus voltage, thereby improving the operation reliability of the frequency converter and having great significance for improving the product quality;
(3) The invention effectively prevents hidden trouble brought by open phase or three-phase unbalance to the frequency converter, avoids adding an extra hardware protection circuit, and further avoids complicacy in circuit design, increase in cost and reduction in reliability.
The invention is described in further detail below with reference to the drawings and the detailed description.
Drawings
FIG. 1-is a topology block diagram of a three-phase power input frequency converter in accordance with the background of the invention;
FIG. 2 is a first waveform diagram of the AC component of the DC bus voltage in the background of the invention;
FIG. 3 is a second waveform diagram of the AC component of the DC bus voltage in the background of the invention;
FIG. 4 is a waveform diagram showing the DC bus voltage with small imbalance of AC components in the prior art;
FIG. 5 is a waveform diagram of the prior art DC bus voltage with a large imbalance of AC components;
FIG. 6 is a diagram showing steps of a method for protecting a phase loss and a three-phase voltage imbalance of a frequency converter according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a control structure of a voltage vector of an ac component of a dc bus voltage according to an embodiment of the present invention.
Detailed Description
The protection method for the open-phase and three-phase voltage unbalance of the frequency converter provided by the invention, as shown in fig. 6, comprises the following steps:
step S1: acquiring a voltage vector of an alternating component of the direct-current bus voltage;
step S2: obtaining the basic value angular frequency of the alternating current component of the direct current bus voltage;
step S3: acquiring the actual angular frequency and amplitude of the alternating current component of the direct current bus voltage;
step S4: judging whether phase loss, unbalance degree of three-phase voltage and whether current limiting treatment is needed or not according to the relation between the actual angular frequency of the alternating current component of the direct current bus voltage and the angular frequency of the power grid;
step S5: if necessary, current limiting protection is performed according to ripple current of the DC bus capacitor when three phases are unbalanced.
In step S1, when acquiring the voltage vector of the ac component of the dc bus voltage, the method includes:
MCU detects direct current busbar voltage V dc Filtering alternating current components by a low pass filter LPF to obtain stable direct current voltageAs shown in equation 1:
wherein omega is LPF The cut-off frequency of the low-pass filter is the power supply voltage frequency omega g 0.1-0.2 times of the number, s is a Lawster operator;
according to the DC bus voltage V dc And stable DC voltageVoltage vector for obtaining AC component>As shown in equation 2:
in the step S2, when acquiring the fundamental angular frequency of the ac component of the dc bus voltage, the method includes:
obtaining voltage vector of DC bus voltage AC componentAnd obtaining a basic value angular frequency according to the MCU sampling time, as shown in a formula 3:
wherein N is the count value of zero crossing point, T s Sampling time omega for MCU 1 Is the base angular frequency.
In the step S3, when acquiring the actual angular frequency and amplitude of the ac component of the dc bus voltage, the method includes:
voltage vector for AC component of DC bus voltageDecomposed into a pair of orthogonal vectors in a stationary coordinate systemAnd->
Will orthonormal vectorAnd->Conversion into orthogonal DC signals V by synchronous rotation of the coordinate system dcd And->And the phase angular frequency delta omega is controlled by proportional integral, and the phase angular frequency delta omega and the fundamental wave angular frequency omega 1 I.e. the actual angular frequency ω;
the actual angular frequency omega is converted into a phase angle theta through an integrator, and the phase angle theta is an angle required by converting a static coordinate system into a synchronous rotation coordinate system; the q-axis component setting value in the synchronous rotation coordinate system is 0 whenWhen the phase-locked loop is equal to 0, the phase locking of the phase-locked loop is stable; d-axis component in synchronous rotation coordinate system>Is the amplitude of the alternating component of the direct current bus voltage.
In the step S4, when judging whether the phase is lost, the unbalance of the three-phase voltage, and the current limiting process is needed, the method includes:
when the actual angular frequency omega and the grid angular frequency omega g The method meets the following conditions: omega is greater than or equal to k 1 ω g When the three-phase input voltage of the power grid is normal, or the voltage unbalance is in an acceptable range, the frequency converter can normally operate;
wherein k is 1 Scaling factors set for the program.
In the step S4, when judging whether the phase is lost, the unbalance of the three-phase voltage, and the current limiting process is needed, the method includes:
when the actual angular frequency omega and the grid angular frequency omega g The method meets the following conditions: omega < k 1 ω g When the three-phase unbalance is serious, the frequency converter is possibly caused to be faulty, and at the moment, ripple current of the direct-current bus capacitor is required to be obtained according to the alternating-current component of the direct-current bus voltage to carry out current limiting treatment;
wherein k is 1 Scaling factors set for the program.
In the step S4, when judging whether the phase is lost, the unbalance of the three-phase voltage, and the current limiting process is needed, the method includes:
when the actual angular frequency omegaAnd grid angular frequency omega g The method meets the following conditions: omega < k 2 ω g When the three-phase unbalance is serious and even the phase failure occurs, the machine is required to be stopped for alarming;
wherein k is 2 Scaling factors set for the program.
In the step S5, when the current limiting protection is performed in the case of three-phase imbalance according to the ripple current of the dc bus capacitor, the method includes:
the actual ripple current of the dc bus capacitor is obtained as shown in equations 4 and 5:
wherein ω is angular frequency, t is time,for phase angle, < >>Is the amplitude of the alternating component of the direct current bus voltage,a voltage vector which is the alternating component of the direct current bus voltage, C is the capacitance of the direct current bus capacitor, i C The actual ripple current of the DC bus capacitor;
and obtaining the peak value of the actual ripple current through the actual ripple current, and carrying out current limiting processing based on the peak value of the actual ripple current.
Further, when the peak value of the actual ripple current is obtained, as shown in equation 6:
wherein I is CM Peak value of actual ripple current;
when current limiting processing is performed based on the peak value of the actual ripple current, the method includes:
when I CM ≤I CM0 -ΔI set1 When the current limiting process is not performed;
when I CM ≤I CMO -ΔI set2 Limiting the load rotation speed to increase so as to limit the ripple current to increase;
when I CM ≥I CM0 When the load rotating speed is reduced, the ripple current is reduced;
when I CM0 -ΔI set2 ＜I CM ＜I CM0 When the current rotating speed is maintained;
wherein I is CM0 Is the rated ripple current of the DC bus capacitor, delta I set1 、ΔI set2 Is the set current threshold.
The invention provides a protection system for phase loss and three-phase voltage unbalance of a frequency converter, which comprises: the device comprises a voltage vector acquisition unit, a basic value angular frequency acquisition unit, an actual angular frequency and amplitude acquisition unit, a phase failure and unbalance degree judgment unit and a current limiting protection unit.
A voltage vector acquisition unit: the voltage vector is used for acquiring the alternating-current component of the direct-current bus voltage;
basic value angular frequency acquisition unit: the base value angular frequency is used for acquiring the alternating current component of the direct current bus voltage;
actual angular frequency and amplitude acquisition unit: the method comprises the steps of acquiring actual angular frequency and amplitude of alternating current components of direct current bus voltage;
phase failure and unbalance degree judging unit: the method is used for judging whether phase loss, unbalance degree of three-phase voltage and whether current limiting treatment is needed or not according to the relation between the actual angular frequency of the alternating current component of the direct current bus voltage and the angular frequency of the power grid;
current limiting protection unit: the current limiting device is used for carrying out current limiting protection when three-phase unbalance is carried out according to ripple current of the direct current bus capacitor when current limiting treatment is needed.
The following examples are further illustrative of the present invention, but the scope of the present invention is not limited thereto.
The implementation of this embodiment is as follows: obtaining voltage vector of DC bus voltage AC component
MCU detects direct current busbar voltage V dc Filtering alternating current components by a low pass filter LPF to obtain stable direct current voltageAs shown in equation 1:
wherein omega is LPF The cut-off frequency of the low-pass filter is the power supply voltage frequency omega g 0.1-0.2 times, s is a Lawster operator.
Then, a voltage vector of the ac component of the dc bus voltage is obtained by the following formula:
the implementation step of this embodiment is: obtaining basic value angular frequency omega of alternating component of direct current bus voltage 1 。
Obtaining voltage vector of DC bus voltage AC componentThe count value N of the zero crossing point of (2) assuming that the MCU sampling time is T s The base angular frequency ω can be found by the following formula 1 ：
The implementation of the embodiment includes the following steps: obtaining the actual angular frequency omega and amplitude of the alternating component of the direct current bus voltage
AC voltage vector in DC bus voltage by phase-locked loop algorithmIs decomposed into a pair of orthogonal vectors under a stationary coordinate system (alpha-beta coordinate system)>And->The pair of orthogonal vectors is then transformed into orthogonal direct current signals by a synchronous rotation coordinate system (d-q coordinate system)>And->And controlling the phase angle frequency Deltaω with the fundamental angular frequency omega by Proportional Integral (PI) 1 I.e. the instantaneous angular frequency of the fundamental wave (actual angular frequency) ω, the actual angular frequency ω is converted by an integrator into a phase angle θ, which is the angle required for the stationary coordinate system to be converted into the synchronous rotating coordinate system. The q-axis component in the synchronous rotation coordinate system is set to 0 when +.>And when the phase-locked loop is equal to 0, the phase of the phase-locked loop is stable. D-axis component in synchronous rotation coordinate system>The control structure is shown in fig. 7 for the amplitude of the fundamental component.
The present embodiment realizes step four: according to the actual angular frequency omega of the alternating current component of the direct current bus voltage and the angular frequency omega of the power grid g And judging whether the phase is out of phase and the imbalance of the three-phase voltage.
Condition one: when omega is greater than or equal to k 1 ω g If the voltage unbalance is within the acceptable range, the frequency converter can normally operate;
condition II: when omega < k 1 ω g When the three-phase unbalance is severe, the frequency converter may be failed, and at the moment, the ripple current of the direct current bus capacitor needs to be calculated according to the alternating current component of the direct current bus voltage to perform current limiting treatment, and the step five is described in detail;
and (3) a third condition: when omega < k 2 ω g When the three-phase unbalance is severe and even the phase failure occurs, the machine needs to be stopped for alarming.
Above k 1 、k 2 The above conditions can also be converted into frequency for comparison for the scaling factor set by the program, and both the angular frequency and the frequency are the same concept and are within the protection scope of the present invention. The present embodiment sets k 1 ＝4，k 2 It is also within the scope of the invention to set other parameters =3.
The invention realizes the step five: and performing current limiting protection in the case of three-phase imbalance according to ripple current of the capacitor.
When the second condition is satisfied, the output power of the load needs to be limited according to the sustainable ripple current capacity of the direct current bus capacitor, so as to achieve the purpose of limiting the ripple current of the capacitor.
Setting rated ripple current of DC bus capacitor as I CM0 The actual ripple current of the DC bus capacitor is i C The peak value of the actual ripple current is I CM The actual ripple current is i C The peak value of the actual ripple current can be obtained according to the formulas (4) and (5), as shown in the formula 6:
then, further current limiting processing is performed according to the formula (6), and the processing mode is as follows:
when I CM ≤I CM0 -ΔI set1 When the current limiting process is not performed;
when I CM ≤I CMO -ΔI set2 Limiting the load rotation speed to increase so as to limit the ripple current to increase;
when I CM ≥I CM0 When the load rotating speed is reduced, the ripple current is reduced;
when I CM0 -ΔI set2 ＜I CM ＜I CM0 When the current rotating speed is maintained;
wherein DeltaI set1 、ΔI set2 The current threshold value is set and adjusted according to actual conditions.
The above embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention are intended to be within the scope of the present invention as claimed.
Claims (10)
1. The protection method for the open-phase and three-phase voltage unbalance of the frequency converter is characterized by comprising the following steps of:
acquiring a voltage vector of an alternating component of the direct-current bus voltage;
obtaining the basic value angular frequency of the alternating current component of the direct current bus voltage;
acquiring the actual angular frequency and amplitude of the alternating current component of the direct current bus voltage;
judging whether phase loss, unbalance degree of three-phase voltage and whether current limiting treatment is needed or not according to the relation between the actual angular frequency of the alternating current component of the direct current bus voltage and the angular frequency of the power grid;
if necessary, current limiting protection is performed according to ripple current of the DC bus capacitor when three phases are unbalanced.
2. The method for protecting against phase loss and three-phase voltage unbalance of a frequency converter according to claim 1, wherein, when acquiring a voltage vector of an ac component of a dc bus voltage, comprising:
MCU detects direct current busbar voltage V dc Filtering alternating current components by a low pass filter LPF to obtain stable direct current voltageAs shown in equation 1:
wherein omega is LPF The cut-off frequency of the low-pass filter is the power supply voltage frequency omega g 0.1-0.2 times of the number, s is a Lawster operator;
according to the DC bus voltage V dc And the stable DC voltageVoltage vector for obtaining AC component>As shown in equation 2:
3. the method for protecting a phase loss and a three-phase voltage unbalance of a frequency converter according to claim 1, wherein when obtaining a fundamental angular frequency of an ac component of a dc bus voltage, the method comprises:
obtaining voltage vector of DC bus voltage AC componentAnd obtaining a basic value angular frequency according to the MCU sampling time, as shown in a formula 3:
wherein N is the count value of zero crossing point, T s Sampling time omega for MCU 1 Is the base angular frequency.
4. The method for protecting against phase loss and three-phase voltage imbalance of a frequency converter according to claim 1, wherein, when obtaining the actual angular frequency and amplitude of the ac component of the dc bus voltage, comprising:
voltage vector for AC component of DC bus voltageDecomposed into a pair of orthogonal vectors in a stationary coordinate system>And
the orthogonal vector is processedAnd->Conversion into orthogonal DC signals by synchronous rotation of the coordinate system>And->And controlling the phase angle frequency Deltaω with the fundamental wave angle frequency omega by proportional integral 1 I.e. the actual angular frequency ω;
the actual angular frequency omega is converted into a phase angle theta through an integrator, wherein the phase angle theta is an angle required by the conversion of the static coordinate system into the synchronous rotation coordinate system; the q-axis component setting value in the synchronous rotation coordinate system is 0 whenWhen the phase-locked loop is equal to 0, the phase locking of the phase-locked loop is stable; d-axis component in said synchronous rotation coordinate system +.>Is the amplitude of the alternating component of the direct current bus voltage.
5. The method for protecting a phase loss and a three-phase voltage unbalance of a frequency converter according to claim 1, wherein when judging whether the phase loss, the unbalance of the three-phase voltage, and the current limiting processing are required, comprising:
when the actual angular frequency omega and the grid angular frequency omega g The method meets the following conditions: omega is greater than or equal to k 1 ω g When the three-phase input voltage of the power grid is normal, or the voltage unbalance is in an acceptable range, the frequency converter can normally operate;
wherein k is 1 Scaling factors set for the program.
6. The method for protecting a phase loss and a three-phase voltage unbalance of a frequency converter according to claim 1, wherein when judging whether the phase loss, the unbalance of the three-phase voltage, and the current limiting processing are required, comprising:
when the actual angular frequency omega and the grid angular frequency omega g The method meets the following conditions: omega < k 1 ω g When the three-phase unbalance is serious, the frequency converter is possibly caused to be faulty, and at the moment, ripple current of the direct-current bus capacitor is required to be obtained according to the alternating-current component of the direct-current bus voltage to carry out current limiting treatment;
wherein k is 1 Scaling factors set for the program.
7. The method for protecting a phase loss and a three-phase voltage unbalance of a frequency converter according to claim 1, wherein when judging whether the phase loss, the unbalance of the three-phase voltage, and the current limiting processing are required, comprising:
when the actual angular frequency omega and the grid angular frequency omega g The method meets the following conditions: omega < k 2 ω g When the three-phase unbalance is serious and even the phase failure occurs, the machine is required to be stopped for alarming;
wherein k is 2 Scaling factors set for the program.
8. The protection method for open-phase and three-phase voltage unbalance of a frequency converter according to claim 1 or 6, characterized by comprising, when current limiting protection is performed in three-phase unbalance according to ripple current of a dc bus capacitor:
the actual ripple current of the dc bus capacitor is obtained as shown in equations 4 and 5:
wherein ω is angular frequency, t is time,for phase angle, < >>Is the amplitude of the alternating component of the direct current bus voltage, < >>A voltage vector which is the alternating component of the direct current bus voltage, C is the capacitance of the direct current bus capacitor, i C The actual ripple current of the DC bus capacitor;
and obtaining the peak value of the actual ripple current through the actual ripple current, and carrying out current limiting processing based on the peak value of the actual ripple current.
9. The protection method for open-phase and three-phase voltage unbalance of a frequency converter according to claim 8, wherein when the peak value of the actual ripple current is obtained, the following formula 6 is adopted:
wherein I is CM Peak value of actual ripple current;
when current limiting processing is performed based on the peak value of the actual ripple current, the method comprises the following steps:
when I CM ≤I CM0 -ΔI set1 When the current limiting process is not performed;
when I CM ≤I CMO -ΔI set2 Limiting the load rotation speed to increase so as to limit the ripple current to increase;
when I CM ≥I CM0 When the load rotating speed is reduced, the ripple current is reduced;
when I CM0 -ΔI set2 ＜I CM ＜I CM0 When the current rotating speed is maintained;
wherein I is CM0 Is the rated ripple current of the DC bus capacitor, delta I set1 、ΔI set2 For a set current threshold。
10. A protection system for a frequency converter open-phase and three-phase voltage imbalance, comprising:
a voltage vector acquisition unit: the voltage vector is used for acquiring the alternating-current component of the direct-current bus voltage;
basic value angular frequency acquisition unit: the base value angular frequency is used for acquiring the alternating current component of the direct current bus voltage;
actual angular frequency and amplitude acquisition unit: the method comprises the steps of acquiring actual angular frequency and amplitude of alternating current components of direct current bus voltage;
phase failure and unbalance degree judging unit: the method is used for judging whether phase loss, unbalance degree of three-phase voltage and whether current limiting treatment is needed or not according to the relation between the actual angular frequency of the alternating current component of the direct current bus voltage and the angular frequency of the power grid;
current limiting protection unit: the current limiting device is used for carrying out current limiting protection when three-phase unbalance is carried out according to ripple current of the direct current bus capacitor when current limiting treatment is needed.
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